I agree with AdamV, the mail server, sbssrv.jfzassoc.com is not accepting connections, so the mail is going to the dnseasy servers (Via the MX priority) and they are not setup for your domain.

Since the connection to sbssrv.jfzassoc.com failed, lets start there. Can you ping the server? Can you verify that it is running? Are all Exchange services running? The Address listed for sbssvr is a public address, from inside the network, can you hit the internal address? If so then this points to a routing issue.

I can not ping sbssrv.jfzassoc.com externally, but I don't know for a fact that I could previously. However, I can not VPN into the server, it never makes a connection. It is definitely running, though. I have LogMeIn access to the server and a desktop in the same office. I can connect to Exchange via an account in Outlook from the internal Desktop. For what it's worth, I can send email out fine through said Exchange account. I don't see any services not running that are an obvious issue to me.
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Charlie W.Jun 2 '10 at 17:05

I think I've figured it out, based on your recommendations. The client told me that the problem happened started over the weekend, and there was a big storm in his area. I checked the router in his office, and it looks like it got set back to defaults. In other words, there are no port forwards set up. Is there a default set of ports that Exchange SBS 2003 uses, or do I need to figure out his custom settings?
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Charlie W.Jun 2 '10 at 17:10

Should be 25 for mail and 80/443 if OWA was set up. I think that should be all.
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Ben PilbrowJun 2 '10 at 19:31

The issue turned out to be that the router in the office somehow (power loss, surge, etc.) got reset to defaults, and got a new IP address to boot. I changed the routing of the sub-domain on the client's host to the new IP address, and recreated all of the necessary port forwards in the router settings. Once the IP change made it through my DNS servers, everything started to work again.

I need to find out if the old IP address was static (which it should have been) and needs to be reconfigured on the router in place of the dynaim one, but I can do that later at night once I know for sure.